Technical Field
The present disclosure relates to an integrated vacuum microelectronic device and fabrication method thereof.
Description of the Related Art
The vacuum tube, once one of the mainstays of electronics, had limitations such as the mechanically fabricated structure inside the glass envelope, preventing miniaturization and integration. For this reason, in the era of systems on chip, it has been gradually supplanted by transistors.
However, in the last years semiconductor fabrication techniques have been used to develop vacuum tube structures in micro miniature form and integrate many of them together. The integrated Vacuum Microelectronic Devices (VMD) have several unique features; they have sub-picosecond switching speeds, operate at temperatures ranging from near absolute zero to hundreds of degrees Celsius, are also very efficient because control is by charge and not by current flow and do not need thermionic emission heaters like in the traditional vacuum discrete devices.
In summary a typical field emission VMD device is made up of a sharply pointed cathode, surrounded by one or more control and/or extraction electrodes, and pointing toward an anode surface. When an appropriate positive potential difference is applied between the cathode and the control electrode, an electric field is generated at the cathode that allows electrons to tunnel through a vacuum space and move towards the anode. The field at the cathode, and hence, the quantity of electrons emitted, can be controlled by varying the control electrode potential.
US005463269 discloses an integrated VMD device and a method for making thereof. The integrated VMD device is made by using a fabrication process in which the conformal deposition of an insulator into a aperture produces a symmetric cusp that can be used as a mold to form a pointed or sharp field emission tip. The aperture can be created out of any stable material including layered alternating stacks of conductors and insulators which can act as the electrodes of the finished devices. Two electrodes (anode and emitter) form a simple diode while three, four and five electrodes would form respectively a triode, tetrode, and pentode for example. Since the cusp is self-aligned within the center of the aperture it is also aligned to the center of these electrodes. The cusp is then filled with an electron-emitting material capable of emitting electrons under the influence of an electric field.
The access aperture created in the electron-emitting material allows the removal of the insulator of the cusp forming layer from the aperture and from underneath the emitter material, thus forming a space and freeing the sharp tip of the emitter (field emission cathode) that was molded by the cusp.
However, the realization of the above described Vacuum Microelectronic Device involves high process flow cost and, nevertheless, said VMD could be affected by some problems which may alter the operative features such ionizing radiations and noise at the power output.